The invention pertains generally to the art of compact, self-propelled, rigid frame, skid-steered vehicles and tractors having hydrostatic transmissions.
1. Description of the Prior Art
In a skid-steered vehicle having dual hydrostatic transmissions, the engine usually drives the two transmissions through a transfer case. The transfer case is mounted between the engine and transmissions. It will have a single input shaft driven by the engine and two output shafts. Two independent hydrostatic transmission pumps, each of the variable delivery, reversible swash plate type, have their input shafts coupled to the respective output shafts of the transfer case. Such an arrangement is disclosed in U.S Pat. No. 3,635,365 filed 20 Feb. 1969 entitled Tractor Vehicle with Hydrostatic Drive Means, inventor James J. Bauer, assigned to the assignee of the present invention.
While this arrangement has proved satisfactory, the limited space problems of compact, skid-steered loaders raises special problems not solved by this construction. As an example, the transfer case takes up room that could be used for other components.
Also, the transfer case is an inherently expensive component requiring its own casting, bearings, shafts and drive elements. In addition the transfer case is partially filled with oil and requires periodic maintenance. Moreover, it adds weight to the machine.
It has also been common practice to simplify the coring or boring of passages in cast parts and instead complicate the hydraulic hosing providing fluid communication between the hydrostatic components. This practice has its advantages in reducing the costs of the casting out in a compact loader further encumbers the available external space with hydraulic lines and fittings.
2. Summary of the Invention
The vehicle will have a body providing a transmission compartment in front of the engine. A series pump unit will be coupled to the engine output shaft on a longitudinal axis centered in the compartment. Hydrostatic motors are mounted at a lower level in the compartment. The axes of rotation of the motors are transverse to the longitudinal axis of the pump unit. The motor output shafts lie between the front and rear axles and drive gear reduction boxes on opposite sides. Drive sprockets within the compartment on the ends of the axles are driven by endless chains driven from output sprockets of the gear boxes.
A body of this type is disclosed in U.S. Pat. No. 3,895,728 entitled "Tractor Vehicle Having Material Handling Subframe", issued 22 July 1975 - inventor John Heggen, and assigned to the assignee of this invention.
By "compact" as used herein, the reference is to a self-propelled vehicle such as disclosed in U.S. Pat. No. 3,231,117 entitled "Tractor Vehicle and Drive Therefor" issued 25 Jan. 1966 and partially assigned to the present assignee and particularly one having a hydrostatic drive as disclosed in the U.S. Pat. No. 3,635,365.
Such a vehicle will normally have a shorter wheel base than the center-to-center distance between the tire threads measured between wheels on opposite sides of the machine. As a result, space limitations are critical because the front and rear axles are closer together than the wheels on opposite sides are far apart. Under conditions where body spaced laterally is wider than it is long the present invention permits the arrangement of the hydrostatic components in a transmission package especially suited for such compact bodies.
In the present invention the series pump unit uses a midplane porting block between a pair of axial piston groups rotatable on a common axis. The porting block has opposed faces against which the piston groups rotate. Arcuate ports in each face on opposite sides of the axis of rotation are in fluid communication with the suction and pressure sides of the piston groups. Internal passages connect the arcuate ports to an external surface of the porting block for connection with hydraulic hose lines to the associated hydrostatic motors. The arrangement of passages is such that at least one passage from each port on the side of the rotational axis opposite the hydrostatic motor with which it is directly connected crosses the rotational axis from one side to the other within the block in reaching the exterior surface thereby eliminating the external crossing of hose lines.
In the preferred embodiment the porting block is situated between two pump sections driven directly by the engine output shaft. The block has an enlarged axial bore aligned with the engine shaft. The rotating piston groups in each pump section are interconnected by a shaft extending through the bore. Means for independently varying the displacement of the rotatable piston groups provides reversible suction and pressure areas on opposite sides of the axis of rotation. The arcuate ports of the porting block are in registry with the suction and pressure areas of the pump sections. These ports are in fluid communication with the corresponding suction and pressure sides of a pair of hydrostatic transmission motors driven by the associated pump sections.
While this is a preferred embodiment of the invention, it will be appreciated that the porting block arrangement is considered novel in itself and could be used to combine either series pumps or motors of the variable or fixed delivery type with equal advantage where the associated hydrostatic components are coupled by hydraulic hose lines in a restricted space.
These and other advantages will be more apparent by referring to the following detailed description which proceeds with a description of the drawings.